The present invention relates to the use of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid ("BHP") as a stabilizer for polyether polyols and for polyurethanes produced from polyether polyols.
Stabilizers or antioxidants for polyethers and polyurethanes are well known and are typically sterically hindered phenols, bisphenols, dialkyl diphenylamines, phenolthiazines, phosphites, and mixtures of compounds of these chemical classes. For example, U.S. Pat. Nos. 4,070,304 and 4,444,676, German Offenlegungsschrift 2,557,619, and European Patent Application 38,876. The efficacy of antioxidants is determined both by the nature of the chemical class (for example, diphenylamines, phenothiazines, and sterically hindered phenols) and by substrate compatibility.
2,6-Di-tert-butyl-4-methylphenol ("BHT") is frequently used for stabilizing polyether polyols, either alone or combined with other compounds of the stabilizer classes described above. Disadvantages of BHT include relatively high volatility and a tendency to migrate into substrates covering the polyurethanes. As a result, a strong yellow coloring develops in the substrates in an atmosphere charged with nitrogen oxides ("NO.sub.x "), such as found in industrial areas or areas with heavy traffic flow. Stabilizers not having these disadvantages are therefore of interest. The object of the present invention is to provide suitable stabilizers. It has been found that 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid is a suitable stabilizer for polyether polyols of molecular weight 300 to 10,000.
Metal salts of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid are described in German Offenlegungsschrift 209,102 for stabilizing organic material, whereby the substrate-dependent efficacy depends to a large extent upon the metal atom used.